Method of forming a photocatalyst and disinfecting a fluid

ABSTRACT

The present disclosure relates to a method of disinfecting a fluid comprising at least one live microbial organism. The method includes contacting the fluid comprising the at least one microbial organism with an effective amount of a photo-catalyst while exposing the fluid and the photo-catalyst to light from at least one light source with a wavelength of about 300-550 nm to reduce the number of the at least one live microbial organism to a predetermined level. The photo-catalyst comprises tungsten trioxide nanoparticles doped with palladium nanoparticles, and the palladium nanoparticles are present in an amount of about 0.1-5% of the total weight of the tungsten trioxide nanoparticles and the palladium nanoparticles.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a Continuation of Ser. No. 15/136,399, nowallowed, having a filing date of Apr. 22, 2016 and which claims priorityto U.S. Provisional Application No. 62/172,698 having a filing date ofJun. 8, 2015 and which is incorporated herein by reference in itsentirety.

BACKGROUND OF THE INVENTION Technical Field

The present disclosure relates to methods of disinfecting a fluid. Morespecifically, the present disclosure relates to a method of disinfectinga fluid by photo-catalytic deactivation of microbial organisms in thepresence of a photo-catalyst comprising tungsten trioxide nanoparticles(n-WO₃) doped with palladium nanoparticles (n-Pd) and a light forphotocatalysis.

Description of the Related Art

The “background” description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description which may nototherwise qualify as prior art at the time of filing, is neitherexpressly nor impliedly admitted as prior art against the presentinvention.

The Word Health Organization (WHO) reports two million deaths worldwideannually due to consumption of microbial organism-infected water.Disinfection of water is therefore critical for human health and theenvironment. Various chemical processes based on activated carbon,coagulation and multimedia sand filtration have been applied forremoving the microorganism. However, these technologies only transferthe contaminated substances from the treated water to another materialthat requires additional treatments and/or disposal. Althoughcost-effective and efficient, chlorination leaves the residual chlorine,which is toxic, in the treated water.

Additionally, disinfection of water in an oil field, e.g. producedwater, is crucial for the quality of oil and protection of oilproduction workers and equipment. For example, sulfate-reducing bacteria(SRB) are an anaerobic microorganism that uses sulfate instead of oxygenfor respiration and can survive and multiply in low oxygen environments.SRB can convert sulfate or sulfite present in water to hydrogen sulfide(H₂S), which combines with iron to form iron sulfide scale. SRBaccumulation increases the corrosiveness of the water in the oil field,and leads to hydrogen blistering or sulfide stress cracking in thepipeline. The corrosion of iron by SRB is rapid, and unlike ordinaryrust, is not self-limiting. Besides being a well-known agent for scaleformation in the oil field installations, SRB can also lead to thedegradation of oil quality with high sulfur content and souring. Thus,deactivation of SRB from the water produced in oil fields is needed toreduce the rust formation, the production of deadly hydrogen sulfide,radioactivity and the degradation of oil quality.

In order to control the growth of SRB, many methods, such as usingbactericides, removing sulfate from water, applying caustic washing toeliminate H₂S, and oxidizing H₂S to elemental sulfur, have been tried.Most of the organic bactericides, such as formaldehyde, phenolic andquaternary amine compounds, glutaraldehyde, chlorine, and acrolein, areharmful to the environment and human health. Additionally, SRB becomeresistant to the bactericides with time, in spite of high doses andrepeated use. A microbiological process of deactivating SRB has alsobeen proposed, where another breed of bacteria, such as denitrifyingbacteria and sulfide-oxidizing bacteria, is introduced to compete withSRB for organic nutrients and inhibit their growth, however, it has notproduced the desired effect due to the complexity of the method.

It is thus an object of the present disclosure to provide a method ofdisinfecting a fluid, e.g. waste water, produced water in an oil field,and sour water from an oil refinery, and more generally, a hydrocarboncontaminated fluid, by photo-catalytic deactivation of microbialorganisms in the presence of a photo-catalyst comprising tungstentrioxide nanoparticles (n-WO₃) doped with palladium nanoparticles (n-Pd)and a light for photocatalysis.

BRIEF SUMMARY OF THE INVENTION

The present disclosure relates to a method of disinfecting a fluidcomprising at least one live microbial organism. The method includescontacting the fluid comprising the at least one microbial organism withan effective amount of a photo-catalyst while exposing the fluid and thephoto-catalyst to light from at least one light source with a wavelengthof about 300-550 nm to reduce the number of the at least one livemicrobial organism to a predetermined level. The photo-catalystcomprises tungsten trioxide nanoparticles doped with palladiumnanoparticles, and the palladium nanoparticles are present in an amountof about 0.1-5% of the total weight of the tungsten trioxidenanoparticles and the palladium nanoparticles.

In one or more embodiments, the palladium nanoparticles have a spheroidshape with an average particle diameter of about 4-17 nm.

In one or more embodiments, the at least one live microbial organism isat least one selected from the group consisting of bacteria, a virus,bacterial spores, protozoa, and fungi.

In one or more embodiments, the at least one light source is at leastone selected from the group consisting of a laser light source, a lightemitting diode, a low pressure mercury lamp, a medium pressure mercurylamp, a high pressure mercury lamp, a xenon lamp, a fluorescent lamp, anincandescent lamp, a sodium vapor lamp, a halogen lamp, a noble gasdischarge, a flame, and sunlight.

In one or more embodiments, the tungsten trioxide nanoparticles have anaverage particle size of 60-100 nm.

In one or more embodiments, the tungsten trioxide nanoparticles have aplate and/or cylindrical shape.

In one or more embodiments, the tungsten trioxide nanoparticles dopedwith the palladium nanoparticles have a lower photoluminescenceintensity at a wavelength of 400-500 nm than tungsten trioxidenanoparticles which are not doped with palladium nanoparticles.

In one or more embodiments, the tungsten trioxide nanoparticles dopedwith the palladium nanoparticles have a first band gap energy, tungstentrioxide nanoparticles which are not doped with palladium nanoparticleshave a second band gap energy, and the difference between the first bandgap energy and the second band gap energy is less than 10% of the secondband gap energy.

In one or more embodiments, the fluid further comprises at least onehydrocarbon, and the live microbial organism is a sulfate-reducingbacterium.

In one or more embodiments, the effective amount of the photo-catalystranges from about 0.5 mg/ml to 1.5 mg/ml of the fluid.

In one or more embodiments, the fluid is treated with at least oneselected from the group consisting of oxygen, ozone, and a peroxidebefore and/or during the contacting and the exposing.

In one or more embodiments, the fluid is contacted with thephoto-catalyst and exposed to the light at a temperature of about 4-100°C. and a pressure of about 0.1-100 bar.

In one or more embodiments, the photo-catalyst is disposed on a surfaceof a substrate to form a photo-catalyst/substrate composite.

In one or more embodiments, the substrate comprises at least oneselected from the group consisting of glass, stone, masonry, a metal,wood, a plastic, concrete, fibers, textiles, yarns, a ceramic, alumina,carbon, silica, an organic polymer, silicon carbide, silicon nitride,boron nitride, zirconium, and tungsten carbide.

In one or more embodiments, the photo-catalyst/substrate composite isdisposed in a fixed bed reactor or fluidized bed reactor and thecontacting involves passing the fluid through the fixed bed reactor orfluidized bed reactor.

In one or more embodiments, the fixed bed reactor comprises a cartridge.

In one or more embodiments, the fixed bed reactor or fluidized reactorfurther comprises at least one adsorbent selected from the groupconsisting of activated carbon, graphite, activated alumina, a molecularsieve, aluminophosphate material, silicoaluminophosphate material,zeolites, faujasite, clinoptilolite mordenite, metal-exchangedsilicoaluminophosphate, uni-polar resin, bi-polar resin, aromaticcross-linked polystyrenic matrix, brominated aromatic matrix, acrylicpolymer, acrylic copolymer, methacrylic polymer, methacrylic copolymer,hydroxyalkyl acrylate, hydroxyalkyl methacrylate, adsorbent carbonaceousmaterial, adsorbent graphitic material, carbon fiber material,nano-material, adsorbent metal salts, alkaline earth metal metallicparticles, ion exchange resin, linear polymers of glucose, andpolyacrylamide.

In one or more embodiments, the method further comprises removing thephoto-catalyst from the fluid after the contacting and the exposing.

In one or more embodiments, the photo-catalyst further comprises atleast one co-catalyst selected from the group consisting of CuO, MoO₃,Mn₂O₃, Y₂O₃, Gd₂O₃, TiO₂, SrTiO₃, KTaO₃, SiC, KNbO₃, SiO₂, SnO₂, Al₂O₃,ZrO₂, Fe₂O₃, Fe₃O₄, NiO, Nb₂O₅, In₂O₅, Ta₂O₅, CeO, and CeO₂.

In one or more embodiments, the co-catalyst is CeO₂, and the molar ratioof tungsten trioxide:CeO₂ in the photo-catalyst lies in the range of 1:5to 5:1.

The foregoing paragraphs have been provided by way of generalintroduction, and are not intended to limit the scope of the followingclaims. The described embodiments, together with further advantages,will be best understood by reference to the following detaileddescription taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the disclosure and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 is a graphical presentation of the XRD patterns of n-WO₃ andn-Pd/WO₃ according to Example 2.

FIG. 2 is a graphical presentation of the XRD patterns of n-TiO₂ andn-Pd/TiO₂ according to Example 2.

FIG. 3 is a TEM image of n-Pd/WO₃ according to Example 2.

FIG. 4 is a TEM image of n-Pd/TiO₂ according to Example 2.

FIG. 5 is a graphical presentation of the EDX spectra of n-Pd/WO₃according to Example 2.

FIG. 6 is a graphical presentation showing the weight percentage of O,Pd, and W in n-Pd/WO₃ according to Example 2.

FIG. 7 is a graphical presentation of the optical absorptivity of n-WO₃and n-Pd/WO₃ in terms of Kubelka-Munk function according to Example 2.

FIG. 8 is a graphical presentation of the optical absorptivity of n-TiO₂and n-Pd/TiO₂ in terms of Kubelka-Munk function according to Example 2.

FIG. 9 is a graphical presentation of the photoluminescence spectrum ofn-WO₃ and n-Pd/WO₃ excited by a light with a wavelength of 350 nmaccording to Example 2.

FIG. 10 is a graphical presentation showing the exponential decay of SRBin water by a laser radiation at 355 nm in wavelength and with 40 mJ perpulse energy in the presence of 1.5 mg/ml of n-Pd/WO₃ according toExample 3.

FIG. 11 is a graphical presentation showing photocatalytic deactivationof SRB in water by a laser radiation at 355 nm in wavelength and with 40mJ per pulse energy in the presence of (a) no photo-catalyst (b) 1.5mg/ml of pure n-WO₃ (c) 0.5 mg/ml of n-Pd/WO₃ (d) 3.0 mg/ml of n-Pd/WO₃(e) 2.0 mg/ml of n-Pd/WO₃ (f) 1.0 mg/ml of n-Pd/WO₃ or (g) 1.5 mg/ml ofn-Pd/WO₃ according to Example 3.

FIG. 12 is a graphical presentation showing the dependence of the SRBdecay rate constant and total depletion time on the concentration ofn-Pd/WO₃ in the SRB contaminated water according to Example 3.

FIG. 13 is an illustration of the photocatalytic deactivation of SRBaccording to Example 3.

FIG. 14 is a graphical presentation showing photocatalytic deactivationof SRB in water by a laser radiation at 355 nm in wavelength and with 40mJ per pulse energy in the presence of (a) no photo-catalyst (b) 1.5mg/ml of n-Pd/TiO₂ (c) 1.5 mg/ml of pure n-WO₃ or (d) 1.5 mg/ml of puren-TiO₂ according to Example 3.

FIG. 15 is a plot of the square root of Kubelka-Munk function multipliedwith energy (KM.eV)^(1/2) versus energy showing the band gap energy of2.48 eV for n-Pd/WO₃ and the band gap energy of 2.66 eV for pure n-WO₃.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present disclosure incorporates by reference in its entirety thefollowing publication: Mohammed A. Gondal, Mohamed A. Dastageer, AmjadB. Khalil, Siddique G. Rashid, and Umair Baig, Photo-catalyticdeactivation of sulfate reducing bacteria—a comparative study withdifferent catalysts and the preeminence of Pd-loaded WO₃ nanoparticles,RSC Adv., 2015, 5, 51399.

The present disclosure provides a method of disinfecting a fluidcomprising at least one live microbial organism. The method includescontacting the fluid comprising the at least one microbial organism withan effective amount of a photo-catalyst while exposing the fluid and thephoto-catalyst to light from at least one light source with a wavelengthof about 100-700 nm, about 150-650 nm, preferably about 200-600 nm, ormore preferably 300-550 nm, or more preferably 325-500 nm, or morepreferably 350-450 nm to reduce the number of the at least one livemicrobial organism to a predetermined level, such as less than 60%, lessthan 50%, less than 40%, less than 30%, less than 20%, less than 10%,less than 5%, or less than 1% of the initial number of the at least onelive microbial organism. The numbers of the live microbial organisms canbe quantified and reported as CFU, or colony forming units. One colonyis formed by a single viable microbial organism when the microbialorganisms are plated at a suitable dilution for single colony formation.This is a standard technique known to microbiologists. Thephoto-catalyst comprises tungsten trioxide nanoparticles (n-WO₃) dopedwith palladium nanoparticles (n-Pd). The palladium nanoparticles arepresent in an amount of about 0.1-5%, or about 0.3-4%, or preferablyabout 0.5-2%, or more preferably about 1% of the total weight of thetungsten trioxide nanoparticles and the palladium nanoparticles.

The disclosed method may photocatalytically deactivate any livemicrobial organisms, including, without limitation, bacteria (e.g. E.coli, sulfate-reducing bacteria, Staphylococcus aureus, Acinetobactor,and Pseudomonas aeruginosa), viruses (e.g. influenza virus, HIV, MS2,and norovirus), bacterial spores (e.g. Clostridium difficile), protozoa(e.g. Giardia), and fungi (e.g. Candida). The disclosed method may alsoadvantageously photocatalytically oxidize and degrade organic andinorganic pollutants present in the fluid.

In some embodiments, the fluid may be microorganism contaminated water,such as river water, lake water, waste water, ground water, or may behydrocarbon contaminated fluids (liquid and/or gas) that includeproduced water in an oil field, a refinery industry effluent (e.g. sourwater), and a chemical industry effluent. In the hydrocarboncontaminated fluid, e.g. produced water and sour water, the hydrocarbonsmay include alkanes, cycloalkanes and various aromatic hydrocarbonsassociated with crude oil, and volatile organic compounds such asbenzene, toluene, ethylbenzene, and xylene. The alkanes, also known asparaffins, are saturated hydrocarbons with straight or branched chainswhich contain only carbon and hydrogen and have the general formulaC_(n)H_(2n+2). They generally have from 5 to 40 carbon atoms permolecule, although trace amounts of shorter or longer molecules may bepresent in the mixture. The cycloalkanes, also known as naphthenes, aresaturated hydrocarbons which have one or more carbon rings to whichhydrogen atoms are attached according to the formula C_(n)H_(2n). Thearomatic hydrocarbons are unsaturated hydrocarbons which have one ormore planar six-carbon rings called benzene rings, to which hydrogenatoms are attached with the formula C_(n)H_(n). The proportion of thehydrocarbons present in the hydrocarbon contaminated fluid may vary, forexample, depending on the oil field where the hydrocarbon contaminatedfluid such as produced water is generated. In some embodiments, theconcentration of the hydrocarbons associated with crude oil in producedwater lies in the range of 1-100 mg/L, or 5-90 mg/L, or 10-80 mg/L, or20-70 mg/L, or 30-60 mg/L, or 40-50 mg/L, and the concentration ofbenzene, toluene, ethylbenzene, and xylene (BTEX) lies in the range of0.5-1500 mg/L, or 1-1000 mg/L, or 10-900 mg/L, or 50-800 mg/L, or100-700 mg/L, or 200-600 mg/L, or 300-500 mg/L, or 350-400 mg/L.

In a preferred embodiment, the fluid is a hydrocarbon contaminatedfluid, e.g. produced water in an oil field, comprising sulfate-reducingbacteria. Sulfate-reducing bacteria (SRB) are an anaerobic microorganismthat plays an important role in biogeochemical processes. SRB usesulfate instead of oxygen for respiration and hence can survive andmultiply in low oxygen environments (See L. L. Barton and G. D. Fauque,Adv. Appl. Microbiol., 2009, 68, 41-98; N. Pfennig, F. Widdel and H. G.Truper, The dissimilatory sulfate reducing bacteria, The Procaryotes. Ahandbook on habitats, isolation and identification of bacteria, SpringerVerlag, New York, 1981; and A. C. Johnson and M. Wood, The ecology andsignificance of sulfate-reducing bacteria in sandy aquifer sediments ofthe London basin, W: Proceedings of International Symposium onSubsurface Microbiology, Bath, Sep. 19-24, 1993, each incorporatedherein by reference in their entirety). SRB can convert sulfate orsulfite present in water to hydrogen sulfide (H₂S), which combines withiron to form iron sulfide scale. SRB accumulation increases thecorrosiveness of produced water in the oil field, and leads to hydrogenblistering or sulfide stress cracking in the pipeline. The corrosion ofiron by SRB is rapid, and unlike ordinary rust, is not self-limiting.Besides being a well-known agent for scale formation in the oil fieldinstallations, SRB can lead to the degradation of oil quality with highsulfur content and souring. Deactivation of SRB from produced water inthe oil fields with the disclosed method can reduce the rust formation,the production of deadly hydrogen sulfide, radioactivity and thedegradation of oil quality.

A photo-catalyst is a material that can activate or change the rate of achemical reaction as a result of exposure to light, such as ultravioletor visible light. When a photo-catalyst absorbs a photon of light havingsufficient energy, an electron can be excited. The resulting“hole/electron” pair is highly reactive and can be coupled to a varietyof reactions that can degrade organic materials. More specifically, anelectron is excited across a band-gap from a valence band to aconduction band when a photon is absorbed by a photo-catalyst and whenthe energy of the photon is equal to or greater than the band gap energyseparating the electrons in the valence band from those in theconduction band. This creates a negatively charged electron in theconduction band and a positively charged hole in the valence band. Whenthe resultant electron-hole pair migrates to the photo-catalyst/fluidinterface, oxidation-reduction processes are initiated. The hole is apowerful oxidizing agent. For instance, the hole can oxidize water tocreate hydroxyl radicals (OH.). Hydroxyl radicals can react with oxygento form superoxide anion (O₂.⁻). Electrons reduce oxygen to variousreactive species including O., O₂., O₂H., HO₂—, H₂O₂ and OH.. Thehydroxyl radical is an extremely potent oxidizing agent (redox potentialof +2.8 V), capable of oxidizing almost all organic compounds. Bycomparison, the redox potentials for the more conventional oxidantschlorine and ozone are +1.36 and +2.07 V, respectively. Hydroxyl radicaland superoxide anion can deactivate a variety of microbial organisms anddegrade a wide variety of organic materials to produce, for example, H₂Oand CO₂. The holes can also oxidize organic materials directly.

In one embodiment, the photo-catalyst comprises tungsten trioxidenanoparticles (n-WO₃), the surface of which is doped or loaded withpalladium nanoparticles. The tungsten trioxide nanoparticles may beprepared by a precipitation method described by S. Supothina, P.Seeharaj, S. Yoriya and M. Sriyudthsak, Ceram. Int., 2007, 33, 931-936,incorporated herein by reference in its entirety. Alternatively, thetungsten trioxide nanoparticles can be synthesized by a variety of othermethods including, but not limited to, solid state reaction, combustion,solvothermal synthesis, pyrolysis (spray and flame), chemical vapordeposition, physical vapor deposition, ball milling, high energygrinding, and plasma synthesis (e.g. radio frequency inductively-coupledplasma (RF-ICP)). Radio frequency inductively-coupled plasma (e.g.thermal) methods as described in U.S. Pat. No. 8,003,563, which isincorporated herein by reference in its entirety, may be useful andpreferable because of low contamination (no electrodes) and highproduction rates and facile application of precursors either in the gas,liquid or solid form. For example, in preparing WO₃ nanoparticles(n-WO₃), a liquid dispersion of ammonium metatungstate in water (5-20 wt% solid in water) can be sprayed into the plasma volume using atwo-fluid atomizer. Preferably, the precursor can be present to about 20wt % solid in water. The plasma can be operated at about 25 kW platepower with argon, nitrogen and/or oxygen gases. The particles formedfrom the condensed vapor from the plasma can then be collected onfilters. In some embodiments, the WO₃ particle surface areas as measuredusing BET range from about 1 m²/g to about 500 m²/g, about 15 m²/g to 30m²/g, or about 20 m²/g. In some embodiments, the obtained n-WO₃ may beheated/calcined from about 200° C. to about 700° C., or about 300° C. toabout 500° C.

In another embodiment, the photo-catalyst may comprise one or moretungsten (W) compounds in place of tungsten trioxide or in addition totungsten trioxide and doped with palladium nanoparticles, with thepalladium nanoparticles present in an amount of about 0.1-5%, or about0.3-4%, or preferably about 0.5-2%, or more preferably about 1% of thetotal weight of the tungsten compound(s) and the palladiumnanoparticles. The tungsten compounds are preferably in the form ofnanoparticles and may include, without limitation, a tungsten oxide,oxycarbide, oxynitride, oxyhalide, or halide, with the tungstencompounds having a +1, +2, +3, +4, +5, +6, +7, or +8 oxidation state orformal charge, or an average oxidation state or formal charge of about+1 to about +8, about +4 to about +8, about +6 to about +8, or about +1to about +4.

In some embodiments, the tungsten trioxide nanoparticles (n-WO₃) mayhave random shapes that include a plate and/or a cylindrical shape, andhave an average particle size of 30-200 nm, or 40-180 nm, or 50-150 nm,or 60-100 nm, or 70-90 nm. The average particle size refers to anaverage length of the longest edge of the tungsten trioxidenanoparticles when the tungsten trioxide nanoparticles have anon-spherical shape, whereas the average particle size refers to anaverage diameter when the tungsten trioxide nanoparticles have aspherical or spheroid shape.

In one embodiment, the tungsten trioxide nanoparticles are doped orloaded with the palladium nanoparticles by a wet incipient method. In anexemplary method, a solution of one or more palladium salts, forexample, palladium nitrate dihydrate (Pd(NO₃)₂.2H₂O) or palladiumacetate in deionized water is poured dropwise with a micropipette ontoWO₃ nanoparticles. The amount of palladium nitrate dihydrate(Pd(NO₃)₂.2H₂O) or palladium acetate is such that palladium metal ispresent in an amount of about 0.1-5%, or about 0.3-4%, or preferablyabout 0.5-2%, or more preferably about 1% of the total weight of thetungsten trioxide nanoparticles and the palladium nanoparticles. Theresultant paste is mixed, dried, and calcinated at 300-500° C. Finally,the obtained product is heated in a programmable furnace for 3 h undercontinuous flow of highly pure hydrogen (99.99%) at 300-400° C. In otherembodiments, the tungsten trioxide nanoparticles may be doped or loadedwith the palladium nanoparticles by photoreduction and sputtering.

In some embodiments, the palladium nanoparticles have a spheroid shapewith an average particle diameter of about 1-30 nm, 2-25 nm, 3-20 nm,4-17 nm, or 5-12 nm. In a preferred embodiment, the palladiumnanoparticles are dispersed on the surface of the tungsten trioxidenanoparticles, providing a high surface area in contact with the lightfor photo-catalytic reaction which generates highly oxidizing radicalssuch as hydroxyl radicals and super-oxide radicals that deactivate themicrobial organisms by oxidizing their cell membrane. In someembodiments, the coverage of the surface of the tungsten trioxidenanoparticles by the palladium nanoparticles is no greater than 90%, nogreater than 80%, or no greater than 60%, or preferably no greater than50%, or more preferably no greater than 30%.

In other embodiments, the tungsten trioxide nanoparticles are doped orloaded with nanoparticles of palladium oxide and/or hydroxide. In someembodiments, the nanoparticles of palladium oxide and/or hydroxide arepresent in an amount of about 0.1-5%, or about 0.3-4%, or preferablyabout 0.5-2%, or more preferably about 1% of the total weight of thetungsten trioxide nanoparticles and the nanoparticles of palladium oxideand/or hydroxide.

In still other embodiments, the photo-catalyst of the present disclosurecomprising the tungsten trioxide nanoparticles doped or loaded with thepalladium nanoparticles may further comprise a co-catalyst. Theco-catalyst includes a material that enhances the photocatalyticproperties of the photo-catalyst. In some embodiments, the co-catalystmay be a compound or a semiconductor that is capable of being reduced byelectron transfer from the conduction band of the photo-catalyst. Forexample, the co-catalyst may have a conduction band having a lowerenergy than the conduction band of the photo-catalyst, or theco-catalyst may have a lowest unoccupied molecular orbital having alower energy than the conduction band of the photo-catalyst. When a termsuch as “lower energy” and “higher energy” is used to compare a band ora molecular orbital of a semiconductor or a photo-catalyst with anotherband or molecular orbital, it means that an electron loses energy whenit is transferred to the band or molecular orbital of lower energy, andan electron gains energy when it is transferred to the band or molecularorbital of higher energy.

In some embodiments, the co-catalyst may be a metal oxide, e.g. CuO,MoO₃, Mn₂O₃, Y₂O₃, Gd₂O₃, TiO₂, SrTiO₃, KTaO₃, SiC, KNbO₃, SiO₂, SnO₂,Al₂O₃, ZrO₂, Fe₂O₃, Fe₃O₄, NiO, Nb₂O₅, In₂O₅, Ta₂O₅, CeO, CeO₂, orcombinations thereof, capable of reducing O₂. For example, it isbelieved that CeO₂ can reduce O₂ gas by electron transfer. In doing so,it is believed that Ce³⁺ transfers an electron to O₂ and is converted toCe⁴⁺ as a result. In one embodiment, the photo-catalyst may transfer anelectron to CeO₂, thus converting Ce⁴⁺ to Ce³⁺, and the Ce³⁺ may thenreduce O₂. Ce³⁺ may also be present as a result of equilibrium processesinvolving CeO₂ and O₂, and superoxide radical ion (O₂.⁻). O₂ andsuperoxide radical ion in such an equilibrium process may be adsorbed tothe surface of solid CeO₂ or present in the atmosphere. Ce³⁺ may also bepresent as a result of oxidation and reduction reactions with ceriumspecies of different oxidation states that may be added intentionally orpresent as impurities.

Any useful ratio of photo-catalyst to co-catalyst may be used. In someembodiments, a photocatalytic composition may have a molar ratio(photo-catalyst:co-catalyst) of about 1:5 to about 5:1, about 1:3 toabout 3:1, about 1:2 to about 2:1, or about 1:1.

In some embodiments, the co-catalyst is CeO₂, and the molar ratio ofWO₃:CeO₂ is about 1:5 to about 5:1, about 1:3 to about 3:1, about 1:2 toabout 2:1, or about 1:1.

In other embodiments, the co-catalyst CeO₂ is doped with Sn, e.g. fromstannous octoate, with the amount of Sn at 1-10 molar %, or 2-8 molar %of the number of moles of CeO₂. The presence of Sn may stabilize theexcited state of the photo-catalyst.

In some embodiments, the co-catalyst may improve the catalyticperformance of the photo-catalyst by increasing the rate ofphotocatalysis by at least about 120%, at least about 150%, at leastabout 180%, at least about 200%, at least about 300%, or at least about500%, as compared to the rate of photocatalysis of the photo-catalyst inthe absence of the co-catalyst.

In some embodiments, the light source may be at least one selected froma laser light source, a light emitting diode (LED), a low pressuremercury lamp, a medium pressure mercury lamp, a high pressure mercurylamp, a xenon lamp, a fluorescent lamp, an incandescent lamp, a sodiumvapor lamp, a halogen lamp, a noble gas discharge, a flame and sunlight.In a preferred embodiment, a laser light source operating in eithercontinuous or pulsed mode and/or an LED are used as a light source.

In some embodiments, the laser light source has one or more of thefollowing types of lasers, without limitation: helium-neon laser, argonlaser, krypton laser, xenon ion laser, nitrogen laser, excimer laser,dye lasers (e.g. stilbene, coumarin 102, rhodamine 6G, etc),helium-cadmium (HeCd) metal-vapor laser, helium-mercury (HeHg)metal-vapor laser, helium-selenium (HeSe) metal-vapor laser,helium-silver (HeAg) metal-vapor laser, strontium vapor laser,neon-copper (NeCu) metal-vapor laser, copper vapor laser, gold vaporlaser, manganese (Mn/MnCl₂) vapor laser, ruby laser, Nd:YAG laser,cerium doped lithium strontium (or calcium) aluminum fluoride (Ce:LiSAF,Ce:LiCAF) laser, and a semiconductor laser (e.g. GaN, InGaN, AlGaInP,AlGaAs, etc).

Compared with a mercury lamp, an LED has a narrower spectral outputcentered around a specific wavelength, e.g. ±10 nm. Additionally, an LEDconverts the input electrical power into useful light, particularly UVlight at a wavelength of less than 400 nm, more efficiently than amercury lamp by generating less heat and light at unwanted wavelengths,e.g. infrared light. Further, an LED has a tighter emission angle than amercury lamp, allowing the majority of the light output to be focuseddirectly where it is required.

The power of any single light source, or the total power of a pluralityof the light sources, and the number of the light sources may varywidely, depending on the volume of the fluid being disinfected, theinitial number and type of the microbial organism in the fluid, the typeof the light source used (e.g. a laser light source, a mercury lamp, oran LED), the way the light sources are placed, e.g. the distance betweenthe light source and a target area of the fluid and the photo-catalystand the distribution of the light in the fluid and the photo-catalyst,the amount and composition of the photo-catalyst contacting the fluid,the wavelength of the light, the disinfection efficiency and/or ratedesired, etc. In a preferred embodiment, the light is monochromatic. Ina preferred embodiment, the light source is a laser light sourceoperating in pulsed mode with a wavelength of 355 nm, and the power ofthe pulsed laser light source is about 0.2-2 mJ/pulse laserirradiation/ml fluid, or about 0.4-1.8 mJ/pulse laser irradiation/mlfluid, or about 0.6-1.5 mJ/pulse laser irradiation/ml fluid, or about0.8-1.2 mJ/pulse laser irradiation/ml fluid. The pulse width of thelaser light may be 3-12 ns, or 5-10 ns, or 7-9 ns. In other embodiments,the power of the light source provides a light intensity in a range of3-500 mW/cm², 20-480 mW/cm², 50-450 mW/cm², 80-400 mW/cm², 100-350mW/cm², 150-300 mW/cm², or 180-250 mW/cm². The photo-catalyticdeactivation of the microbial organism in the fluid by the disclosedmethod entails an interaction between the light and the photo-catalyst,since the light alone without the photo-catalyst may result in a muchslower deactivation rate of the microbial organism (e.g. thedeactivation rate with only the light may be 1/200, 1/150, 1/100, 1/50,1/30, 1/20, 1/10, 1/5/or 1/3 of the deactivation rate with both thelight and the photo-catalyst interacting with each other), and since thephoto-catalyst without the light may result in no deactivation of themicrobial organism, as observed by A. Bagabas, M. Gondal, A. Khalil, A.Dastageer, Z. Yamani, and M. Ashameri, Laser-induced photocatalyticinactivation of coliform bacteria from water using pd-loaded nano-WO₃,10th International Symposium “Scientific Bases for the Preparation ofHeterogeneous Catalysts”, 2010, incorporated herein by reference in itsentirety.

In a preferred embodiment, the light from the light source has awavelength of 300-550 nm and interacts with the photo-catalyst in thepresence of water and oxygen. The interaction between the light and thephoto-catalyst generates electrons and holes (h⁺). The electrons reduceO₂ to form super oxide radicals, while the holes oxidize H₂O to formhydroxyl radicals. Both the super oxide radicals and the hydroxylradicals damage or kill the microbial organisms in the fluid by, forexample, oxidizing the cell membrane of the microbial organisms.Additionally, the light in the ultraviolet light wavelength range(10-400 nm) can convert O₂ to O₃ that in turn produces highly reactivehydroxyl radicals. O₂ may be from atmospheric air and/or other sources,such as an O₂ gas tank, from which O₂ may be pumped or injected into thefluid before and/or while the fluid and the photo-catalyst are exposedto the light. Water may be present in the fluid, or may be introducedinto the fluid in the form of liquid water or water vapor. Because thesuper oxide radicals and particularly the hydroxyl radicals are alsoeffective in oxidizing and decomposing dyes (e.g. anthocyanins,methylene blue, and basic blue 41), surfactants, volatile organiccompounds (e.g. methane, ethane, propane, butane, benzene, ethylbenzene,toluene, acetone, diethyl ether, methanol, ethanol, isopropyl alcohol,formaldehyde, acetaldehyde formaldehyde, propionaldehyde, ethyl acetate,and xylene), small organic molecules (e.g. caffeine, diclofenac,ibuprofen, geosmin, flumequine, naphthalene, anthracene, salicylic acid,phenol, 2-chlorophenol, 4-chlorophenol, benzoic acid, 2-naphthol, andfluorescein), organometallic compounds, crude oil that containshydrocarbons including alkanes, cycloalkanes and various aromatichydrocarbons, NO_(x) (e.g. NO, NO₂, N₂O, and HONO), SO_(X) (e.g. SO₂,and SO₃), CO, O₃, soot, algae, eggs of aquatic organisms, and planktoniclarvae, the disclosed method can be used advantageously to disinfect, aswell as remove toxic pollutants from, industrial waste water, forexample, a hydrocarbon contaminated waste water or fluid, particularlyproduced water, which may contain 1-100 mg/L, or 5-90 mg/L, or 10-80mg/L, or 20-70 mg/L, or 30-60 mg/L, or 40-50 mg/L of hydrocarbonsassociated with crude oil and 0.5-1500 mg/L, or 1-1000 mg/L, or 10-900mg/L, or 50-800 mg/L, or 100-700 mg/L, or 200-600 mg/L, or 300-500 mg/L,or 350-400 mg/L of benzene, toluene, ethylbenzene, and xylene (BTEX),and sour water, from the petro-chemical industry.

Sour water is the wastewater produced during many refining processes. Ittypically contains hydrogen sulfide and ammonia, which must be removedby sour water strippers before the water can be reused elsewhere in therefinery or sent to a wastewater system. Besides hydrogen sulfide(typically at 300-12,000 ppm by weight) and ammonia (typically at100-8,000 ppm by weight), sour water may also contain phenol (typicallyup to 300 ppmw), hydrogen cyanide (at variable concentrations, e.g.10-20 ppmw), selenium, organic acids, caustic substances, mineral acids,hydrocarbons, chlorides, sulfates, and mercaptans. Because of the likelypresence of sulfates, hydrocarbons, and phenol in sour water, thedisclosed method may be advantageously used to treat sour water incombination with the sour water strippers that effectively removeammonia and hydrogen sulfide but not phenol hydrogen cyanide, and manyhydrocarbons, particularly heavier hydrocarbons. In one embodiment, thedisclosed method may be used to treat sour water to photo-catalyticallydeactivate microbial organisms, particularly sulfate-reducing bacteriawhat are likely present in sour water containing sulfates, and tooxidize and degrade at least some of the phenol, hydrogen cyanide, andhydrocarbons in the sour water before the sour water is fed to the sourwater strippers. The advantage of this pre-treatment of the sour waterwith the disclosed method is to reduce or eliminate any potentialgeneration of additional hydrogen sulfide by sulfate reducing bacteriaafter the sour water stripper treatment, reduce the amount of thehydrocarbons potentially contacting the sour water strippers (sour wateris usually de-oiled before entering the sour water strippers), andreduce the amounts of phenol and hydrogen cyanide, which are almost notremoved in the sour water strippers, in the stripped water. In anotherembodiment, the disclosed method may be used to treat sour waterstripped of hydrogen sulfide and ammonia (after the sour water strippertreatment) to remove phenol, hydrogen cyanide, and hydrocarbons anddeactivate microbial organisms, particularly sulfate-reducing bacteria,from the stripped water. In still another embodiment, the disclosedmethod may be used to treat sour water before the treatment with sourwater strippers as well as the stripped water after the sour waterstripper treatment. The phenol in the sour water is preferably deeplyoxidized and decomposed to water and carbon dioxide, and the hydrogencyanide in the sour water is preferably oxidized to cyanate (NCO), whichis safer than cyanide, by the disclosed method.

In another preferred embodiment, the fluid, for example, a hydrocarboncontaminated fluid, produced water, and sour water, is treated with atleast one selected from the group consisting of ozone, and peroxides,for example, hydrogen peroxide, before and/or while the fluid and thephoto-catalyst are exposed to the light.

The light, preferably with a wavelength of 300-550 nm, more preferablywith a wavelength in the UV range of 300-400 nm, may interact withozone, preferably in the presence of water, to produce hydroxyl radicalsthat oxidize and deactivate the microbial organisms in the fluidindependent of the photo-catalyst, as disclosed by Katarina Šilhárovä,Ján Derco, Peter Tölgyessy, Mária Valičlcová, Michal Melicher, Reducingof organic petroleum compounds in water by ozonation/UV processes, 45thInternational Petroleum Conference, Jun. 13, 2011, Bratislava, SlovakRepublic, incorporated herein by reference in its entirety. In someembodiments, the concentration of O₃ in the fluid is about 0.1-5 mg/L,about 0.2-4.5 mg/L, about 0.5-4 mg/L, about 0.8-3 mg/L, or about 1-2mg/L.

The light, preferably with a wavelength of 300-550 nm, more preferablywith a wavelength in the UV range of 300-400 nm, may convert peroxides,e.g. H₂O₂, to hydroxyl radicals that oxidize and deactivate themicrobial organisms in the fluid independent of the photo-catalyst. Inone embodiment, the fluid is pre-treated with H₂O₂ before contacting thephoto-catalyst and being exposed to the light. In another embodiment,the fluid is treated with H₂O₂ while contacting the photo-catalyst andbeing exposed to the light. In still another embodiment, the fluid ispretreated with H₂O₂, and is treated with additional H₂O₂ whilecontacting the photo-catalyst and being exposed to the light to replacethe consumed H₂O₂ and keep a H₂O₂ concentration of at least 40%, atleast 50%, at least 60%, at least 70%, or at least 80% of the initialH₂O₂ concentration. Since H₂O₂ is thermodynamically unstable anddecomposes to form water and oxygen (2H₂O₂→2 H₂O+O₂), with the rate ofdecomposition increasing with rising temperature, concentration and pH,the disclosed disinfection method may be preferably performed at a lowambient temperature (e.g. 4-30° C., preferably 10-25° C., or preferably15-20° C.) and/or under a high pressure condition to inhibit H₂O₂decomposition and/or keep O₂ from escaping from the fluid, e.g. under apressure greater than an ambient pressure of about 1 bar, such as 2-100bar, or 5-90 bar, or 10-80 bar, or 15-70 bar, or 20-60 bar, or 30-50bar. The fluid may be treated with H₂O₂ by adding a H₂O₂ containingsolution to the fluid, or by pumping or injecting a H₂O₂ containingsolution or vapor into the fluid. The initial concentration of the H₂O₂in the fluid may be about 0.2-4 g/L, about 0.4-3 g/L, or about 0.6-2g/L. The pH of the fluid is preferably in the acidic range of about 1-6,preferably about 2-5, or more preferably about 3.

In one embodiment of the method, the contacting of the fluid with thephoto-catalyst may be performed by mixing an effective amount of thephoto-catalyst with a certain volume of the fluid, preferably with themixture under constant agitation (e.g. stirring, shaking, or vortexing),while exposing the mixture to the light. The effective amount of thephoto-catalyst per unit volume of the fluid may vary depending on thecomposition of the photo-catalyst, the initial number and the type ofthe microorganism in the fluid, the wavelength of the light and type ofthe light source, the extent or efficiency of contact between thephoto-catalyst and the light determined by the distribution of the lightand the photo-catalyst in the fluid, the disinfection efficiency andrate desired, etc, and may typically range from about 0.1-3 mg/ml, or0.3-2 mg/ml, or 0.5-1.5 mg/ml of the fluid. In some embodiments, thelight source may be placed in such a way that it is not in directcontact with the fluid/photo-catalyst mixture, for example, the lightsource may be placed on top of, on a side of, and/or underneath a vesselcontaining the mixture, with the light traveling from the light sourceto reach the mixture, or a portion thereof, preferably unimpeded, andwith the vessel walls preferably made of materials substantiallytransparent to the light, e.g. light transparent glass or plastic. Thedistance between the light source and a target area of the mixture mayvary, depending on the desired power level or intensity of the light thefluid and the photo-catalyst are exposed to and the desired lightcoverage of the fluid and the photo-catalyst. To adjust the lightcoverage of the fluid and the photo-catalyst when the light source is alaser light source, a set of lenses and mirrors may be used to increasethe diameter of the laser beam from the laser light source, for example,to 0.5-10 cm, 1-8 cm, 2-6 cm, or 3-4 cm. The light source may bestationary or may be in motion to increase the light coverage of thefluid and the photo-catalyst. In other embodiments, the light source maybe placed in a way that it is in direct contact with thefluid/photo-catalyst mixture, for example, the light source may beimmersed in the mixture of the fluid and the photo-catalyst. The lightsource may be stationary or may be in motion. These are preferredembodiments when more power of the light is desired to penetrate thefluid and reach the photo-catalyst.

In another embodiment, the photo-catalyst comprising the tungstentrioxide nanoparticles (n-WO₃) doped with the palladium nanoparticles isdisposed on a surface of a substrate to form a photo-catalyst/substratecomposite with a photo-catalyst layer or a coating that can come intocontact with the light and the material (e.g. microbial organisms,organic compounds, etc) to be deactivated and/or decomposed. In someembodiments, the thickness of the photo-catalyst layer or coating is1-200 μm, or 10-180 μm, or 30-150 μm, or 50-120 μm, or 80-100 μm. Thesubstrate may comprise any suitable material which is inert or stable inthe fluid during the disclosed photo-catalytic disinfection process andwhich provides a surface for the deposition of the photo-catalyst.Non-limiting examples of the suitable substrate material include glass(e.g. borosilicate glass, soda glass, or quartz), stone, masonry, metals(e.g. stainless steel, gold, aluminum, titanium, copper, and variousmetal alloys), woods, plastics (e.g. polycarbonate, polystyrene, nylon,and polyethylene), concrete, fibers, textiles, yarns, ceramics, alumina,carbon, silica, organic polymers, silicon carbide, silicon nitride,boron nitride, zirconium, and tungsten carbide. In some embodiments, thephoto-catalyst covers at least about 30%, at least about 50%, at leastabout 70%, at least about 90%, or at least about 95% of the substratesurface. Since the photo-catalyst is dispersed on the surface thesubstrate, by contacting the fluid with the photo-catalyst/substratecomposite, this embodiment may advantageously increase the surface areaof the photo-catalyst interacting with both the microbial organisms tobe deactivated in the fluid and the light to more effectively producethe oxidative radicals to deactivate the microbial organisms in thefluid. In a preferred embodiment, the placement of the light source issuch that uniform illumination of the photo-catalyst within the volumeof the fluid to be treated is achieved. In another preferred embodiment,the substrate does not block illumination of the volume of the fluid tobe treated. Thus, the volume fraction of the substrate is kept tominimal and/or has high transparency to the activating photons. Toenhance volumetric illumination, the substrate material is preferablymade from glass or other materials transparent or semi-transparent tothe photo-activating wavelengths described above.

In one embodiment, the photo-catalyst layer or coating directly contactsthe substrate.

In another embodiment, if the photo-catalyst is known to react with thesubstrate it is attached to, a protective layer may be included thatkeeps the photo-catalyst from directly contacting the substrate, forexample, when the reactive species (e.g., hydroxyl radicals) that allowthe photo-catalyst to deactivate the microbial organisms that settle ona surface can also degrade the surface if the surface (e.g., plastic)includes materials that are susceptible to attack by the reactivespecies. In this case, apatite can be used as a protective layer. Inanother embodiment, the photo-catalyst can be encapsulated in aprotective layer. Further discussion of these techniques can be found inJP2008-088436 and U.S. Pat. No. 6,217,999, each incorporated herein byreference in its entirety.

By being disposed upon the substrate, the photo-catalyst can be aseparately formed layer, formed prior to disposition upon the substrate.In another embodiment, the photo-catalyst layer or coating can be formedon the substrate surface by, for example, without limitation, vapordeposition, chemical vapor deposition, physical vapor deposition,laminating, pressing, rolling, soaking, melting, gluing, sol-geldeposition, spin coating, dip coating, bar coating, brushing coating,sputtering, thermal spraying, flame spray, plasma spray, high velocityoxy-fuel spray, atomic layer deposition, cold spraying, aerosoldeposition, or sputtering. In still another embodiment, thephoto-catalyst can be incorporated into the surface of the substrate,e.g., at least partially embedded within the surface.

In a preferred embodiment where the photo-catalyst further comprises theco-catalyst CeO₂, a dispersion comprising the photo-catalyst, CeO₂, adispersing media (e.g. water, methanol, or ethanol), and optionally abinder may be made with the molar ratio of the photo-catalyst to CeO₂being between 1-99 molar %, or 20-80 molar %, or 40-60 molar %photo-catalyst and 99-1 molar %, or 80-20 molar %, or 60-40 molar %CeO₂; wherein the dispersion has about 2-50 wt %, or about 5-40 wt %, orabout 10-30 wt %, or about 15-25 wt %, or about 20 wt % solid materials.The dispersion may be homogenized by ultrasound. After the dispersion isapplied to a substrate, the dispersion and the substrate may be heatedat a sufficient temperature and length of time to evaporatesubstantially all the dispersing media from the dispersion. In someembodiments, the dispersion is applied to cover the substrate, either inwhole or in part, or to a surface of the substrate to create a coatingor surface layer. In some embodiments, at least 90%, at least 95%, atleast 99% of the dispersing media is removed. In another embodiment, thedispersion covered substrate is heated at a temperature between aboutroom temperature and 500° C. In another embodiment, the dispersioncovered substrate is heated at a temperature between about 90° C. andabout 150° C. In another embodiment, the dispersion covered substrate isheated at a temperature of about 120° C. While not wanting to be limitedby theory, it is believed that keeping the temperature below 500° C. mayreduce the possibility of thermal deactivation of the photo-catalystand/or co-catalyst, for example, due to dopant diffusion, dopantinactivation, loaded material decomposition or coagulation (reduction intotal active surface area). In another embodiment, the dispersioncovered substrate is heated for a time between about 10 seconds andabout 2 hours. In another embodiment, the mixture covered substrate isheated for a time of about 1 hour.

The dispersions described herein can be applied to virtually anysubstrate. Other methods of applying the dispersion to a substrate caninclude slot/dip/spin coating, brushing, rolling, soaking, melting,gluing, or spraying the dispersion on a substrate. A proper propellantcan be used to spray a dispersion onto a substrate.

In one embodiment, the photo-catalytic surface of thephoto-catalyst/substrate composite may be in contact with the fluid bybatch mixing the photo-catalyst/substrate composite with the fluid,preferably under constant agitation (e.g. stirring, shaking, orvortexing). In other embodiments, the photo-catalyst/substrate compositemay be in the form of granular particles, which can be installed in afixed bed reactor or fluidized bed reactor. The fluid can be applied toa fixed bed column or reactor of the photo-catalyst/substrate compositeto come into contact with the photo-catalytic surface of the compositewhile the fluid and the photo-catalyst/substrate composite are exposedto the light from the light source, which can be stationary or in motionand which may be placed in direct contact with the fluid and thephoto-catalyst/substrate composite or not, and the effluent of thecolumn or reactor comprises the treated fluid with reduced numbers ofthe live microbial organisms. In some embodiments, the fixed bed reactorof the photo-catalyst/substrate composite comprises a cartridge for easycarry and use. For example, such a cartridge can be attached to a faucetof ground water, or installed in a container where wastewater or ahydrocarbon contaminated liquid containing the microbial organismspasses through the cartridge from an upper level of the container, withthe disinfected wastewater or hydrocarbon contaminated liquid exitingthe cartridge at a lower level of the container with reduced numbers ofthe microbial organisms. Further, the fixed bed reactor and cartridge,and the fluidized bed reactor described below can include adsorbentsbesides the photo-catalyst/substrate composite, such as activatedcarbon, graphite, activated alumina, a molecular sieve, aluminophosphatematerial, silicoaluminophosphate material, zeolites, fauj asite,clinoptilolite, mordenite, metal-exchanged silicoaluminophosphate,uni-polar resin, bi-polar resin, aromatic cross-linked polystyrenicmatrix, brominated aromatic matrix, acrylic polymer, acrylic copolymer,methacrylic polymer, methacrylic copolymer, hydroxyalkyl acrylate,hydroxyalkyl methacrylate, adsorbent carbonaceous material, adsorbentgraphitic material, carbon fiber material, nano-material, adsorbentmetal salts (including, but not limited to perchlorates, oxalates, andalkaline earth metals), alkaline earth metal metallic particles, ionexchange resin, linear polymers of glucose, polyacrylamide, or acombination thereof, to advantageously adsorb from the fluid biologicalcontaminants such as bacterial toxins and bacterial cell debris, harmfulpollutants such as benzene, xylene, toluene, phenol, ethyl benzene andtheir photo-catalytic oxidation products that may still be toxic, heavymetal ions and dyes. In a preferred embodiment, the adsorbent isinstalled in a part of the fixed bed, cartridge, or fluidized bed thatis separate from and downstream of the part of the fixed bed, cartridge,or fluidized bed where the photo-catalyst/substrate composite isinstalled to avoid interference with the exposure of the fluid and thephoto-catalyst/substrate composite to the light by the adsorbent and tofacilitate adsorption of the biological contaminants released by thedeactivated microbial organisms.

Alternatively, the photo-catalyst/substrate composite can form afluidized bed reactor with the fluid comprising the microbial organisms,for example, by introducing the pressurized fluid, either in a liquidform, or in a gaseous form, or in a mixed liquid and gaseous form,through the particulate medium of the photo-catalyst/substratecomposite. In the fluidized bed reactor, contact between thephoto-catalyst and the fluid is greatly enhanced while both are exposedto the light, as compared to a fixed bed column or reactor, leading to ahigher photo-catalytic deactivation efficiency and/or rate of themicrobial organisms in the fluid. In a fluidized bed reactor, the lightsource can be likewise stationary or in motion and can be placed indirect contact or not with the mixture of the fluid and thephoto-catalyst/substrate composite.

Whether the contacting of the fluid with the photo-catalyst/substratecomposite is effected by batch mixing, and/or fixed or fluidized bedreactor, the fluid flow over the photo-catalytic surface of thecomposite is preferably turbulent to improve mixing and mass transferrates between the microbial organisms/organic and/or inorganiccontaminants and the oxidizing species generated at the photo-catalystsurface. One way to induce a turbulent fluid flow over thephoto-catalytic surface of the photo-catalyst/substrate composite is byagitating the fluid while it is contacting the photo-catalyst/substratecomposite. Another way is by providing a geometric configuration of thecomposite to result in such a turbulent fluid flow. An exemplaryconfiguration is a helix axially disposed on a rod as illustrated inFIG. 5 of International Patent Application Publication No. WO2002083570A1, incorporated herein by reference in its entirety. The purpose ofsuch a geometric configuration or the like is to enhance turbulent flowby creating counter-rotating vortices, cross-current mixing, divisionand recombination of fluid, and otherwise mixing and agitating the fluidstream.

A mass of the photo-catalyst, or more preferably thephoto-catalyst/substrate composite, can be pressed, molded, or packagedinto a variety of forms to facilitate photo-catalytic deactivation ofthe microbial organisms in the fluid and/or removal of thephoto-catalyst or the photo-catalyst/substrate composite from thedisinfected fluid when the photo-catalytic deactivation is complete,and/or when the photo-catalytic activity of the photo-catalyst isdiminished or exhausted. Non-limiting examples of the forms include agranule, a pellet, a sphere, a powder, a woven fabric, a non-wovenfabric, a mat, a felt, a block, and a honeycomb.

In some embodiments, the method further comprises removing thephoto-catalyst or the photo-catalyst/substrate composite from thedisinfected fluid. For example, the photo-catalyst/composite in powderform may be injected into a storage tank of the fluid comprising themicrobial organisms and then removed from the disinfected fluid byfiltration, centrifugation, or settling. The photo-catalyst/substratecomposite in fiber form may be inserted in a section of the fluid (e.g.waste water, a hydrocarbon contaminated liquid) treatment piping ortrench, and be removed for recycling or disposal when the disinfectionis complete or the photo-catalytic activity of the photo-catalyst hasbeen exhausted.

In another embodiment, the method of disinfecting a fluid may take aform of a continuous and/or multi-stage process. For example, multiplefixed bed columns or reactors of the above mentionedphoto-catalyst/substrate composite or, more broadly, multipledisinfection units of any suitable modes or configurations and theircombinations, e.g. batch mixing of the photo-catalyst/substratecomposite with the fluid accompanied by the simultaneous exposure of themixture to the light, passing of the fluid through a fixed bed reactor,a cartridge, and/or a fluidized bed reactor of thephoto-catalyst/substrate composite accompanied by the simultaneousexposure of the photo-catalyst/substrate composite and the fluid to thelight, etc., can be set up to deactivate the microbial organisms in thefluid in a parallel and/or sequential manner. In some embodiments, thedisinfection columns, reactors, or units set up in the parallel fashionmay be standby columns, reactors, or units ready to replace another setof parallel columns, reactors, or units whose disinfection capacityaffected by the photo-catalytic activity of the photo-catalyst and/orother factors has been exhausted to make the disinfection continuous.The photo-catalyst/substrate composite in replaced columns, reactors, orunits may be recycled and reused or disposed of. In other embodiments,the disinfection columns, reactors, or units set up in the sequential orserial fashion allow microbial organisms in the fluid to be deactivatedthrough multiple stages to achieve a high disinfection efficiency. Sincethe disinfection efficiency and/or rate may be affected by the amount ofthe photo-catalyst per unit volume of the fluid, the multipledisinfection units may preferably contain different amounts of thephoto-catalyst or photo-catalyst/substrate composite per unit volume ofthe fluid such that a preferred amount of the photo-catalyst or thephoto-catalyst/substrate composite resulting in the maximum disinfectionefficiency and/or rate may be included and determined and furtheradjustments to amount of the photo-catalyst or thephoto-catalyst/substrate composite in the disinfection units may be madeaccordingly to improve the overall disinfection efficiency and/rateamong all the units.

The time during which the fluid contacts the photo-catalyst (or thephoto-catalyst/substrate composite) while the fluid and thephoto-catalyst (or the photo-catalyst/substrate composite) are exposedto the light may vary, depending on, without limitation, the contactingmode (e.g. batch mixing, fixed bed reactor type, or fluidized reactortype), and the contacting and photo-catalytic deactivation conditions(e.g. the agitation speed, the amount and composition of thephoto-catalyst, the power and type of the light source, the distributionand intensity of the light the fluid and the photo-catalyst are exposedto, the type and initial number of the microbial organism in the fluid,and the disinfection efficiency desired).

In some embodiments, the fluid is contacted with the photo-catalystwhile the fluid and the photo-catalyst are exposed to the light at atemperature of about 4-100° C., preferably about 10-90° C., preferablyabout 15-80° C., preferably about 20-70° C., or preferably about 25-60°C., or preferably 30-50° C.

In some embodiments, the fluid is contacted with the photo-catalystwhile the fluid and the photo-catalyst are exposed to the light at apressure of about 0.1-100 bar, about 0.5-80 bar, preferably about 1-60bar, preferably about 1-40 bar, preferably about 1-20 bar, or preferablyabout 1-10 bar.

In some embodiments, the disclosed method using the tungsten trioxidenanoparticles doped with the palladium nanoparticles as thephoto-catalyst disinfects the fluid, i.e. reduces the number of the atleast one live microbial organism in the fluid to a predetermined level,at a rate that is at least 10 times, at least 20 times, at least 30times, at least 40 times the rate by a substantially similar method witha photo-catalyst comprising non-palladium nanoparticle doped tungstentrioxide nanoparticles, e.g. the precursor tungsten trioxidenanoparticles prior to being doped with the palladium nanoparticles tomake the tungsten trioxide nanoparticles (n-WO₃) doped with thepalladium nanoparticles (n-Pd). The advantageously high photo-catalyticdisinfection activity exhibited by the palladium nanoparticle-dopedtungsten trioxide nanoparticles as compared to non-palladiumnanoparticle-doped tungsten trioxide nanoparticles is unexpected inlight of the currently known key factors believed to enhancephoto-catalytic activity of a photo-catalyst, particularly band gapenergy. For example, in a previous study by M. A. Gondala, A. Bagabasb,A. Dastageera, A. Khalil, Synthesis, characterization, and antimicrobialapplication of nano-palladium-doped nano-WO₃, Journal of MolecularCatalysis A: Chemical 323 (2010) 78-83, incorporated herein by referencein its entirety, a photo-catalyst comprising tungsten trioxidenanoparticles doped with palladium nanoparticles at 10 wt % of the totalweight of the tungsten trioxide nanoparticles and the palladiumnanoparticles has a higher photo-catalytic activity in disinfection ofE. Coli in water than a photo-catalyst comprising the non-palladiumnanoparticle doped precursor tungsten trioxide nanoparticles, and theincreased photo-catalytic activity of the n-Pd doped tungsten trioxidenanoparticles is associated with a higher band gap energy of 3.5 eVrelative to the band gap energy of 2.71 eV of the non-n-Pd dopedprecursor tungsten trioxide nanoparticles. It is believed that theincreased band gap energy present in the n-Pd doped tungsten trioxidenanoparticles inhibits electron-hole recombination, resulting in moreeffective electron-hole pairs for the generation of the oxidizingradicals. In the present disclosure, likely due to a lower loading ofthe palladium nanoparticles on the tungsten trioxide nanoparticles, i.e.the tungsten trioxide nanoparticles are doped with the palladiumnanoparticles at 0.1-5 wt % of the total weight of the tungsten trioxidenanoparticles and the palladium nanoparticles, not only the increase inband gap energy of the n-Pd-doped tungsten trioxide nanoparticles ascompared to the band gap energy of the non-n-Pd-doped precursor tungstentrioxide nanoparticles may be much smaller or insignificant, asevidenced by similar peak emission wavelengths in the photoluminescencespectra of the n-Pd-doped tungsten trioxide nanoparticles and thenon-n-Pd-doped precursor tungsten trioxide nanoparticles followingexcitation by a light with a wavelength of 350 nm (See FIG. 9 in thefollowing Example 2 as an example), but also the band gap energy of then-Pd-doped tungsten trioxide nanoparticles may be unexpectedly lowerthan that of the non-n-Pd-doped precursor tungsten trioxidenanoparticles (see FIG. 15 in the following Example 3 as an example). Insome embodiments, the increase in band gap energy present in the n-Pddoped tungsten trioxide nanoparticles may be less than 20%, less than10%, less than 5% of the band gap energy of non-n-Pd-doped tungstentrioxide nanoparticles. In other embodiments, the band gap energy of then-Pd-doped tungsten trioxide nanoparticles may be 70-95%, 75-90%, or80-85% of the band gap energy of non-n-Pd doped tungsten trioxidenanoparticles. On the other hand, the tungsten trioxide nanoparticlesdoped with the palladium nanoparticles of the present disclosure have anunexpectedly lower photoluminescence intensity than non-n-Pd dopedtungsten trioxide nanoparticles (Also see FIG. 9 in the followingExample 2 as an example), indicative of a reduction in electron-holerecombination and thus an increase in effective electron-hole pairs togenerate oxidizing radicals. In some embodiments, the photoluminescenceintensity of the tungsten trioxide nanoparticles doped with thepalladium nanoparticles may be about 10-80%, 20-70%, or about 30-60%, orabout 40-50%, of the photoluminescence intensity of non-n-Pd dopedtungsten trioxide nanoparticles at a wavelength of 350-550 nm, or400-500 nm, or 425-475 nm following excitation by a light with awavelength of 350 nm.

Having generally described this invention, a further understanding canbe obtained by reference to certain specific examples which are providedherein for purposes of illustration only and are not intended to belimiting unless otherwise specified.

Example 1 Materials and Methods

1. Synthesis of the Nano Photo-Catalysts

Pure WO₃ nanoparticles (n-WO₃) were prepared by precipitation method asreported by Supothina et al (See S. Supothina, P. Seeharaj, S. Yoriyaand M. Sriyudthsak, Ceram. Int., 2007, 33, 931-936, incorporated hereinby reference in its entirety). Briefly, pre-determined amount ofammonium tungstate pentahydrate ((NH₄)₁₀—W₁₂O₄₁.5H₂O) was dissolved indeionized water by heating at 85° C. and this was followed by dropwiseaddition of warm and concentrated nitric acid (HNO₃, Merck) withvigorous stirring. The obtained precipitates, after settling down for 24hours, were thoroughly washed with deionized water. Finally, theprecipitates were filtered by centrifugation, dried and calcined at 500°C. for 6 h at a ramp rate of 1° C. min⁻¹. TiO₂ nanoparticles (n-TiO₂)were synthesized by using decomposition-precipitation technique.Specifically, a titanium (III) sulfate solution (Sigma-Aldrich) wasadded into hot sulfuric acid. The resultant solution was precipitated byadding excess amount of urea followed by heating at 90° C. Theprecipitates were thoroughly washed and calcined at 400° C. for 3 h at aramp rate of 1° C. min⁻¹. In the loading process, the prepared n-WO₃nanoparticles were loaded with palladium nanoparticles (n-Pd) by wetincipient technique. A highly concentrated solution of palladium nitratedihydrate (Pd(NO₃)₂.2H₂O) in deionized water was poured dropwise with amicropipette on the WO₃ nanoparticles, and the resultant paste wasmixed, dried and calcinated at 400° C. Finally, the obtained product washeated in a programmable furnace for 3 h under a continuous flow ofhighly pure hydrogen (99.99%) at 350° C. A similar procedure was carriedout for loading of n-Pd on the TiO₂ nanoparticles.

2. Material Characterization

The crystal structure of the synthesized photo-catalysts was analyzedwith a wide angle X-ray diffractometer (Philips X'Pert PRO 3040/60)equipped with a Cu-Kα radiation source in a 2θ=20° to 2θ=90° range. Thetransmission electron microscopy (TEM) images were recorded with TitanG2 80-300 (FEI Company, Hillsboro, USA), operated at a primary beamenergy of 300 keV, while a point-to-point analysis was performed at thesame beam energy with a step of 0.235 nm. Elemental analysis wasperformed to confirm the palladium loading using energy dispersiveanalyzer unit (EDAX) coupled with field emission scanning electronmicroscopy (FE-SEM, TESCAN FERA3). A charge coupled device (CCD) camera(US4000, Gatan, Inc., Pleasanton, Calif.) was used to record digitalimages. A JASCO, V-670, UV-vis-NIR spectrophotometer was used forrecording the solid-state absorption and diffused reflectance spectra(DRS) of the synthesized photo-catalysts using BaSO₄ pellet as areference. The photoluminescence spectra were recorded using Shimadzuspectrofluorometer with 1200 grooves per mm.

3. Photo-Catalytic Reaction Studies

The reaction cell had two 2-inch diameter quartz windows that let thelaser beam in and out of the sample and at the same time withstood highenergy laser pulse. The emerging laser beam was blocked with a laserbeam block. The different photo-catalyst concentration was maintained byadding different amounts of the photo-catalyst in the sulfate-reducingbacteria (SRB) infected water and the reaction cell was kept on amagnetic stirrer which kept the photo-catalyst homogeneously dispersedin the infected water. A high power laser beam with a wavelength of 355nm and a pulse width of about 8 ns generated from the third harmonic ofthe Spectra Physics Nd:YAG laser (Model GCR 250) was employed as aradiation source. The destructive effects of the focused laser beam wereminimized and the maximum interaction between the photons and thesemiconductor material (i.e. the photo-catalyst) was ensured byexpanding the diameter of the beam to 2 cm with a set of lenses andmirrors. An aliquot of the laser irradiated sample was collected at aregular interval for bacteria counting.

4. Culturing and Counting of Bacteria

ATCC 1249 medium, modified Baar's medium for sulfate reducers componentwas prepared and used for the growth of SRB. The medium was autoclavedand the nitrogen gas was bubbled through the medium for about 30 minutesto remove the dissolved oxygen in the medium. The medium was transferredto anaerobic chamber with a clean nitrogen environment where inoculationtook place. After distributing the medium to the flasks with the desiredvolume of 100 ml per flask, each flask was inoculated with SRB brothfrom a one-week old culture. The inoculum to medium volume ratio was 1%.After the SRB containing medium in the flask was incubated at 30° C. for7 days, 80 ml of the SRB containing medium with or without aphoto-catalyst was irradiated by exposing the medium to the laserradiation with the wavelength of 355 nm and with 40 mJ per pulse energy.A 1-ml aliquot of the irradiated medium was transferred to a new steriletube at a regular interval. The medium in the new sterile tube collectedat each time point was serially diluted, and 100 μl of each dilutedsample was directly plated on an agar plate (in duplicates) for SRBcolony formation followed by incubation for 7 days at 30° C. After theincubation, the plate was observed under a colony counter and the numberof colonies was visually recorded (See J. Wen, D. Xu, T. Gu and I. Raad,World J. Microbiol. Biotechnol., 2012, 28, 431-435; E. A. Ghazy, M. G.Mahmoud, M. S. Asker, M. N. Mahmoud, M. M. Abo Elsoud and M. E. AbdelSami, Water, Am. J. Sci., 2011, 7, 604-608; each incorporated herein byreference in its entirety).

Example 2

Characterization of the Photo-Catalysts

1. Morphological Characterization of the Photo-Catalysts

The XRD patterns for the synthesized n-WO₃ and n-Pd/WO₃ are presented inFIG. 1. All the main indexed peaks were fitted to the hexagonal WO₃system (JCPDS card 35-1001). Higher diffraction coming from [001]compared with other planes suggests that [001] is the major growthdirection. After n-Pd loading on n-WO₃, no change in XRD pattern wasnoticed, indicating the material is of a single phase and is impurityfree. The Pd diffraction not appearing in the XRD pattern could be dueto a high dispersion and a low loading (around 1 wt %) of Pdnanoparticles on the n-WO₃. However, the crystallinity of n-Pd/WO₃ wasreduced probably due to the dispersed palladium covering n-WO₃. The XRDpatterns of n-TiO₂ and n-Pd/TiO₂ are presented in FIG. 2. All the peakscan be indexed to anatase phase of TiO₂, and the [101] is the majorgrowth zone. After n-Pd loading, no extra peak was noticed probably dueto the low loading of n-Pd (around 1 wt %) and a high dispersion of n-Pdon the surface of n-TiO₂. TEM analysis of n-Pd/WO₃ revealed that the WO₃nanoparticles had an average particle size of 60-100 nm and had plateand cylindrical like morphologies, and that the palladium nanoparticles(n-Pd) with an average particle size of 4-17 nm were anchored on the WO₃nanoparticles as shown in FIG. 3. The TiO₂ nanoparticles werequasi-spherical and had an average particle size of 20-30 nm, and thepalladium nanoparticles with spheroid morphologies were dispersed on thesurface of the TiO₂ nanoparticles as shown in FIG. 4. Referring to FIG.5 and FIG. 6 for the energy-dispersive X-ray spectroscopy (EDX) spectrumand quantitative results of n-Pd/WO₃, respectively, the n-Pd/WO₃contained Pd in addition to W and O, confirming that the surface of theWO₃ nanoparticles was successfully loaded with n-Pd.

2. Optical Characterization of the Photo-Catalysts

The optical properties of n-WO₃ and n-Pd/WO₃, n-TiO₂ and n-Pd/TiO₂ wereestimated by applying Kubelka-Munk transformation on the reflectancedata acquired by diffuse reflectance spectroscopy. The opticalabsorbance in terms of Kubelka-Munk function is estimated using thefollowing equation:

$\begin{matrix}{{F(R)} = \frac{\left( {1 - R} \right)^{2}}{2(R)}} & (1)\end{matrix}$where R is the diffuse reflectance. Two opposing changes in theabsorption curves brought about by the n-Pd loading were observed fromFIG. 7 and FIG. 8: (i) enhanced visible light absorption and (ii) aslight blue shift in the absorption edge (i.e. the wavelength at whichthe onset of absorption occurred) following the loading of n-Pd onn-TiO₂ and n-WO₃. The enhancement of the visible light absorption isattributed to the surface plasmon absorption of larger palladiumnanoparticles and clusters, while the blue shift in the absorption edgecould be the result of smaller Pd nanoparticles (about 6 nm) absorbinglight in the UV region (See K. Hayat, M. A. Gondal, M. M. Khaled, Z. H.Yamani and S. Ahmed, J. Hazard. Mater., 2011, 186, 1226-1233,incorporated herein by reference in its entirety). Photoluminescence(PL) spectra of both n-WO₃ and n-Pd/WO₃ are shown in FIG. 9, where thereis a substantial reduction in PL intensity upon the n-Pd loading onn-WO₃, indicating a reduction of electron-hole pair recombinationbrought about by the n-Pd loading on the WO₃ nanoparticles.

Example 3 Photocatalytic Deactivation of SRB Using the n-WO₃, n-Pd/WO₃,n-TiO₂, and n-Pd/TiO₂ Photo-Catalyst

FIG. 10 is a typical exponential decay curve of SRB representing thefastest SRB deactivation process obtained while using 1.5 mg/ml ofn-Pd/WO₃ with a laser radiation at 355 nm in wavelength and at 40 mJ perpulse energy. The rate of deactivation of SRB was convenientlyquantified in terms of the decay rate constant k (i.e. the slope of thelinear lnN/N₀ versus time plot, where N is the number of SRB at time tand N₀ is the initial number of SRB) in the units of minute⁻¹ and thetotal depletion time t_(d) (time required for the complete depletion) inthe units of minutes. FIG. 11 indicates that the rate of SRBdeactivation depended on the n-Pd/WO₃ concentrations. Specifically, thedecay rate constant initially increased with the increasingconcentration of n-Pd/WO₃, reached the maximum when the concentration ofn-Pd/WO₃ was at 1.5 mg/ml, and started to decline when the concentrationof n-Pd/WO₃ was further increased to 2 mg/ml and to 3 mg/ml. For all thedecay curves in the present disclosure, the laser radiation at 355 nm inwavelength and with the pulse energy of 40 mJ was used. The initial SRBcount (N₀) was fixed to be 4×10⁷ counts per ml, and any SRB count below150 counts per ml (corresponding to a value equal to −11.5 on theordinate axes) was taken as complete depletion. Referring to FIG. 11,when the SRB depletion curves obtained with no photo-catalystrepresented by line (a), with 1.5 mg/ml of pure n-WO₃ represented byline (b), and with 1.5 mg/ml of n-Pd/WO₃ represented by line (g) werecompared, the decay rate constant increased from nearly zero with nophoto-catalyst to 0.18 minute⁻¹ with 1.5 mg/ml of pure n-WO₃ and to themaximum of 5.4 minute⁻¹ with 1.5 mg/ml of n-Pd/WO₃. Additionally, thedecay rate constant with n-Pd/WO₃ as the photo-catalyst at everyconcentration tested was more than that with 1.5 mg/ml of pure n-WO₃ asthe photo-catalyst. The increased decay rate constant with n-Pd/WO₃ maybe attributed to the increased optical absorption following the n-Pdloading depicted in FIG. 7. As the decay rate constant increased, thetime required for the total depletion decreased. For example, in thepresence of 1.5 mg/ml of pure n-WO₃, it would take 64 minutes for thetotal depletion of SRB from the contaminated water, whereas it wouldtake just 2 minutes for the total depletion of SRB from the contaminatedwater with 1.5 mg/ml of n-Pd/WO₃, indicating an advantageous enhancementof the photo-catalytic SRB deactivation with n-Pd/WO₃. FIG. 12 shows thetrends of both the SRB decay rate constant (k) and the total depletiontime (t_(d)) with the concentration of n-Pd/WO₃ in the SRB contaminatedwater.

With an increase in photon absorption of the catalytic material, aphoto-catalyst may generate more electron-hole pairs that move to thesurface of the photo-catalyst particle to form highly oxidizingradicals, such as hydroxyl radicals and superoxide radicals, whicheffectively oxidize the cell membrane and damage the microbial organisms(See Y. Xiong, J. Chen, B. Wiley, Y. Xia, Y. Yin and Z. Y. Li, NanoLett., 2005, 5, 1237-1242, incorporated herein by reference in itsentirety). FIG. 13 depicts the proposed mechanism of the photo-catalyticdeactivation of SRB. The hydroxyl radicals may generate oxygen while H⁺ions may form hydrogen by capturing the conduction band electrons. Thesuperoxide radicals and hydroxyl radicals generated through the laserinduced photocatalysis process killed the bacteria in contaminatedwater. This deactivation process of bacteria is effective as long as thecell membrane of the bacteria is exposed to the superoxide and hydroxylradicals. When the concentration of the photo-catalyst increases beyonda certain level, the photo-catalyst particles may mask the bacterialsurface, preventing the radicals from effectively oxidizing thebacterial cell membrane. In a photocatalysis process, the electron-holepairs generated are prone to recombination and any technique inhibitingthe recombination can make more electron-hole pairs available for thephotocatalytic reaction. The reduced photoluminescence signal exhibitedby n-Pd/WO₃ as compared to pure n-WO₃ indicates a substantial reductionin electron-hole recombination in n-Pd/WO₃, resulting in more effectiveelectron-hole pairs available for the deactivation process of SRB.

For comparison, the SRB decay curves were obtained with 1.5 mg/ml ofn-Pd/TiO₂ and 1.5 mg/ml of pure n-TiO₂ as well as with no photo-catalystand with 1.5 mg/ml of pure n-WO₃ as shown in FIG. 14. A comparison ofthe SRB decay curve with pure n-TiO₂ to that with n-Pd/TiO₂ indicatesthat the n-Pd loading on n-TiO₂ resulted in a reduction in the bacterialdecay rate constant from 0.2 minute⁻¹ to 0.12 minute⁻¹ rather than animprovement in the photo-catalytic activity, in contrast to the n-Pdloading on n-WO₃. Further, although n-TiO₂ was a better photo-catalystthan n-WO₃ for SRB deactivation, the n-Pd loading on n-TiO₂ inhibitedthe photo-catalytic deactivation activity of n-TiO₂, whereas the n-Pdloading on n-WO₃ substantially enhanced the photo-catalytic deactivationactivity of n-WO₃ shown in FIG. 11.

The results above indicate that the mere presence of Pd in aphoto-catalyst would not necessarily increase photo-catalyticdeactivation of SRB. To effect increased photo-catalytic deactivation ofSRB, the n-Pd loading on a photo-catalyst needs to result in a change inthe structure of the band gap that enables the increased lightabsorption and decreased electron-hole recombination. Referring to FIG.15, the band gap energy of n-Pd/WO₃ and pure n-WO₃ was determined byplotting the square root of Kubelka-Munk function multiplied with energy(KM·eV)^(1/2) versus energy. The band gap energy of n-Pd/WO₃ was 2.48eV, which was unexpectedly lower than the band gap energy of 2.66 eV forpure n-WO₃. The lower band gap energy of n-Pd/WO₃ relative to that ofpure n-WO₃ would not have predicted the increased photo-catalyticdeactivation activity of n-Pd/WO₃ relative to pure n-WO₃ based on, forexample, the publication of M. A. Gondala, A. Bagabasb, A. Dastageera,A. Khalil, Synthesis, characterization, and antimicrobial application ofnano-palladium-doped nano-WO₃, Journal of Molecular Catalysis A:Chemical 323 (2010) 78-83, described previously in the presentdisclosure.

The SRB decay rate constants k and the depletion time t_(d) fordifferent photo-catalysts and at different concentrations of thephoto-catalysts are shown in Table 1. Table 1 also shows the thresholdtime, which is defined as the time taken after excitation for the onsetof photo-deactivation of SRB. For the SRB deactivation with n-Pd/WO₃ atdifferent concentrations, the threshold times were instant, whereas thethreshold times were 20 minutes with no photo-catalyst present, 6minutes with pure n-WO₃, 8 minutes with n-Pd/TiO₂, and 2 minutes withpure n-TiO₂.

TABLE 1 Catalytic performance indicators for the disinfection of SRB incontaminated water Catalyst Decay rate Total Threshold concentrationconstant depletion time time Catalyst (mg ml⁻¹) (k) (min⁻¹) (minutes)(minutes) No catalyst N/A 0.05 220 20  Pure n-WO₃ 1.5 0.18 64 6 n-Pd/WO₃0.5 0.21 55 Instant n-Pd/WO₃ 1 1.14 10 Instant n-Pd/WO₃ 1.5 5.40 2Instant n-Pd/WO₃ 2 0.58 20 Instant n-Pd/WO₃ 3 0.27 43 Instant Puren-TiO₂ 1.5 0.20 58 2 n-Pd/TiO₂ 1.5 0.12 92 8

In light of the differences in the photo-catalytic activity for SRBdeactivation between n-Pd/WO₃ and n-WO₃, between n-Pd/TiO₂ and n-TiO₂,and between n-Pd/WO₃ and n-Pd/TiO₂, as represented by their decay rateconstants listed in Table 1, it appears that the slight blue shift inthe absorption edge, probably due to the absorption of smaller Pdnanoparticles, and the enhancement of the visible light absorption,probably due to the surface plasmon absorption or resonance of larger Pdnanoparticles and clusters, that were seen in both n-Pd/WO₃ andn-Pd/TiO₂ relative to their respective non-n-Pd doped n-WO₃ and n-TiO₂as shown in FIG. 7 and FIG. 8, may not or may only partially account forthe increased photo-catalytic activity of n-Pd/WO₃ relative to n-WO₃. Itis well known that the surface plasmon resonance is a process involvinga crucial interplay between concerted oscillations of free electronstrapped on the surface of a photo-catalyst and the electromagnetic wavesand very sensitive to the size, shape, composition and arrangement of ametallic nanostructure (See T. Y. Leung, C. Y. Chan, C. Hu, J. C. Yu andP. K. Wong, Water Res., 2008, 42, 4827-4837; S. Balci, C. Kocabas, S.Ates, E. Karademir, O. Salihoglu and A. Aydinli, Phys. Rev. B: Condens.Matter Mater. Phys., 2012, 86, 235402; Y. J. Bao, B. Zhang, Z. Wu, J. W.Si, M. Wang, R. W. Peng, X. Lu, J. Shao, Z. F. Li, X. P. Hao and N. B.Ming, Appl. Phys. Lett., 2007, 90, 251914-251917; H. J. Chen, X. S. Kou,Z. Yang, W. H. Ni and J. F. Wang, Langmuir, 2008, 24, 5233-5237; G.Park, C. Lee, D. Seo and H. Song, Langmuir, 2012, 28, 9003-9009; M. S.Yavuz, G. C. Jensen, D. P. Penaloza, T. A. P. Seery, S. A. Pendergraph,J. F. Rusling and G. A. Sotzing, Langmuir, 2009, 25, 13120-13124; eachincorporated herein by reference in its entirety). Additionally, theblue shift of the absorption edge in the absorption spectra followingthe n-Pd loading on n-WO₃ appears too small to account for thesubstantial enhancement in the photo-catalytic SRB deactivation activityexhibited by n-Pd/WO₃. On the other hand, the higher photo-catalyticactivity of n-Pd/WO₃ relative to n-WO₃ correlated with the significantlyreduced photoluminescence signal in n-Pd/WO₃ as shown in FIG. 9,indicative of a reduced electron-hole pair recombination. By contrast,the n-Pd loading on n-TiO₂ resulted in no significant change in thephotoluminescence signal, correlating with no improvement in thephoto-catalytic SRB deactivation activity of n-Pd/TiO₂ relative ton-TiO₂.

The invention claimed is:
 1. A method of forming a photocatalyst anddisinfecting a fluid comprising at least one live microbial organismwith the photocatalyst, the method comprising: preparing WO₃nanoparticles by adding nitric acid to an aqueous solution of ammoniumtungstate, loading the WO₃, nanoparticles with palladium nanoparticlesby adding a solution of palladium nitrate to the WO₃ nanoparticles thendrying and calcining to form the photocatalyst, contacting the fluidcomprising the at least one microbial organism with an effective amountof a photo-catalyst while exposing the fluid and the photo-catalyst tolight from at least one light source with a wavelength of about 300-550nm to reduce the number of the at least one live microbial organism to apredetermined level, wherein the photo-catalyst comprises tungstentrioxide nanoparticles doped with palladium nanoparticles, wherein thepalladium nanoparticles are present in an amount of about 0.1-5% of thetotal weight of the tungsten trioxide nanoparticles and the palladiumnanoparticles, and wherein the tungsten trioxide nanoparticles dopedwith the palladium nanoparticles have a first band gap energy, tungstentrioxide nanoparticles which are not doped with palladium nanoparticleshave a second band gap energy, and wherein the difference between thefirst band gap energy and the second band gap energy is less than 10% ofthe second band gap energy.
 2. The method of claim 1, wherein thepalladium nanoparticles have a spheroid shape with an average particlediameter of about 4-17 nm.
 3. The method of claim 1, wherein thetungsten trioxide nanoparticles have an average particle size of 60-100nm.
 4. The method of claim 1, wherein the tungsten trioxidenanoparticles have a plate and/or cylindrical shape.
 5. The method ofclaim 1, wherein the tungsten trioxide nanoparticles doped with thepalladium nanoparticles have a lower photoluminescence intensity at awavelength of 400-500 nm than tungsten trioxide nanoparticles which arenot doped with palladium nanoparticles.
 6. The method of claim 1,wherein the photo-catalyst is disposed on a surface of a substrate toform a photo-catalyst/substrate composite.
 7. The method of claim 1,further comprising removing the photo-catalyst from the fluid after thecontacting and the exposing.
 8. The method of claim 1, wherein thephoto-catalyst further comprises at least one co-catalyst selected fromthe group consisting of CuO, MoO₃, Mn₂O₃, Y₂O₃, Gd₂O₃, TiO₂, SrTiO₃,KTaO₃, SiC, KNbO₃, SiO₂, SnO₂, Al₂O₃, ZrO₂, Fe₂O₃, Fe₃O₄, NiO, Nb₂O₅,In₂O₅, Ta₂O₅, CeO, and CeO₂.
 9. The method of claim 8, wherein theco-catalyst is CeO₂, and wherein the molar ratio of tungsten trioxide:CeO₂ in the photo-catalyst lies in the range of 1:5 to 5:1.